As you might notice while you use the Google Chrome debugger, every file in an extension is also accessible by an absolute URL like this:

chrome-extension://<extensionID>/<pathToFile>

In that URL, the <extensionID> is a unique identifier that the extension system generates for each extension. You can see the IDs for all your loaded extensions by going to the URL chrome://extensions. The <pathToFile> is the location of the file under the extension's top folder; it's the same as the relative URL.